Method for assigning PTRS for phase noise removal in wireless communication system, and device therefor

ABSTRACT

A method for a base station to transmit a signal allowing a terminal to remove phase noise in an mmWave communication system, according to an embodiment of the present specification, may be provided. Here, the method for transmitting a signal for removing phase noise comprises: a step of generating a phase tracking reference signal (PTRS) and a first RS; a step of assigning the PTRS and the first RS to a resource block; and a step of transmitting the assigned PTRS and first RS, wherein the step of assigning the PTRS and the first RS includes a step of changing a frequency location of the PTRS if the PTRS and the first RS collide in the resource block, wherein the changed PTRS frequency location may be changed to a frequency location, across frequencies on which a predetermined demodulation reference signal (DMRS) port, associated with the PTRS, in a DMRS port group is located, which is closest to the existing PTRS frequency location and avoids collision with the first RS.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 ofInternational Application No. PCT/KR2018/003461, filed on Mar. 23, 2018,which claims the benefit of U.S. Provisional Application No. 62/476,744,filed on Mar. 25, 2017, 62/518,566, filed on Jun. 12, 2017, and62/520,666, filed on Jun. 16, 2017, the contents of which are all herebyincorporated by reference herein in their entireties.

TECHNICAL FIELD

The present disclosure relates to a wireless communication system, andmore particularly, to a method of allocating a phase tracking referencesignal (PTRS) for phase noise cancellation in a wireless communicationsystem and device therefor.

BACKGROUND ART

An ultra-high frequency radio communication system using a millimeterwave (mmWave) is configured to operate at a center frequency in therange of several GHz to several tens of GHz. Due to such a centerfrequency feature, significant path loss may occur in a shadow area inthe mmWave communication system. Considering that a synchronizationsignal should be stably transmitted to all terminals within the coverageof a base station, the synchronization signal needs to be designed andtransmitted in consideration of the potential deep-null phenomenon,which may occur due to the above-described ultra-high frequency bandcharacteristic, in the mmWave communication system.

DISCLOSURE Technical Problem

The present disclosure is contrived to solve the aforementionedproblems. Accordingly, an object of the present disclosure is to providea PTRS allocation method.

Another object of the present disclosure is to improve a phase noisecancellation procedure for a user equipment (UE) in a wirelesscommunication system to accurately decode a received signal.

A further object of the present disclosure is to provide a method ofimproving the efficiency of signal transmission for phase noisecancellation.

Still another object of the present disclosure is to improvereceiving-side operation by providing information on signal transmissionfor phase noise cancellation.

Still a further object of the present disclosure is to provide a methodof transmitting a signal for phase noise cancellation by consideringphase noise compensation and reference signal overhead.

Technical Solution

In an aspect of the present disclosure, provided herein is a method oftransmitting, by a base station, a signal for enabling a user equipment(UE) to eliminate phase noise in a millimeter wave (mmWave)communication system. The method may include: generating a phasetracking reference signal (PTRS) and a first reference signal (RS);allocating the PTRS and the first RS to a resource block; andtransmitting the allocated PTRS and first RS. Allocating the PTRS andthe first RS may include, when the PTRS collides with the first RS inthe resource block, shifting a frequency location of the PTRS. Theshifted PTRS frequency location may correspond to a frequency locationcapable of avoiding the collision with the first RS and closest to thecurrent PTRS frequency location among frequency locations at which aspecific demodulation reference signal (DMRS) port in a DMRS port groupassociated with the PTRS is positioned.

In another aspect of the present disclosure, provided herein is a basestation for transmitting a signal for enabling a UE to eliminate phasenoise in a mmWave communication system. The base station may include: areceiver configured to receive a signal from an external device; atransmitter configured to transmit a signal to an external device; and aprocessor configured to control the receiver and the transmitter. Theprocessor may be configured to: generate a PTRS and a first RS; allocatethe PTRS and the first RS to a resource block; and transmit theallocated PTRS and first RS. When the PTRS and the first RS areallocated, if the PTRS collides with the first RS in the resource block,the processor may be configured to shift a frequency location of thePTRS. The shifted PTRS frequency location may correspond to a frequencylocation capable of avoiding the collision with the first RS and closestto the current PTRS frequency location among frequency locations atwhich a specific DMRS port in a DMRS port group associated with the PTRSis positioned.

The followings are commonly applicable to the method and device fortransmitting a signal for phase noise cancellation in a mmWavecommunication system.

When the PTRS and the first RS are allocated to a plurality of resourceblocks, shifting the frequency location of the PTRS may be performedindependently in each of the plurality of resource blocks.

The specific DMRS port may be equal to a DMRS port in the DMRS portgroup associated with the PTRS.

The specific DMRs port may correspond to any one of at least one DMRSport included in the DMRS port group associated with the PTRS.

The first RS may include at least any one of a channel stateinformation-reference signal (CSI-RS), a sounding reference signal(SRS), and a tracking RS. The shifted PTRS frequency location may beindicated by at least any one of radio resource control (RRC), a mediumaccess control-control element (MAC-CE), and downlink controlinformation (DCI).

When a frequency location capable of avoiding the collision with thefirst RS is not found among frequency locations at which DMRS ports inthe DMRS port group associated with the PTRS are positioned, the PTRSmay be positioned at a frequency location capable of avoiding thecollision among frequency locations closest to the current PTRSfrequency location.

When the PTRS collides with the first RS in the resource block, thefrequency location of the PTRS may be fixed and a time-domain locationthereof may be shifted.

Only when the PTRS is allocated at an interval of at least oneorthogonal frequency-division multiplexing (OFDM) symbol at onefrequency, the frequency location of the PTRS may be fixed and thetime-domain location thereof may be shifted.

When the frequency location capable of avoiding the collision with thefirst RS is not found among the frequency locations at which the DMRSports in the DMRS port group associated with the PTRS are positioned, ifthe PTRS is allocated at an interval of at least one OFDM symbol at onefrequency, the frequency location of the PTRS may be fixed and thetime-domain location thereof may be shifted. In addition, when thefrequency location capable of avoiding the collision with the first RSis not found among the frequency locations at which the DMRS ports inthe DMRS port group associated with the PTRS are positioned, if the PTRSis allocated to all OFDM symbols at one frequency, the frequencylocation of the PTRS may be shifted to the frequency location capable ofavoiding the collision among the frequency locations closest to thecurrent PTRS frequency location.

When the frequency location capable of avoiding the collision with thefirst RS is not found among the frequency locations at which the DMRSports in the DMRS port group associated with the PTRS are positioned,the frequency location of the PTRS may be fixed and the time-domainlocation thereof may be shifted. If the collision with the first RS isstill unavoidable after shifting of the time-domain location, thefrequency location of the PTRS may be shifted to the frequency locationcapable of avoiding the collision among the frequency locations closestto the current PTRS frequency location.

Advantageous Effects

According to the present disclosure, a received signal can be accuratelydecoded by improving a phase noise cancellation procedure for a UE in awireless communication system.

According to the present disclosure, a method of improving theefficiency of signal transmission for phase noise cancellation can beprovided.

According to the present disclosure, receiving-side operation can beimproved by providing information on signal transmission for phase noisecancellation.

According to the present disclosure, a PTRS allocation method can beprovided.

According to the present disclosure, a method of transmitting a signalfor phase noise cancellation by considering compensation for phase noiseand reference signal overhead can be provided.

It will be appreciated by persons skilled in the art that the effectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and other advantages ofthe present disclosure will be more clearly understood from thefollowing detailed description.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 2 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 3 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 4 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 5 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 6 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 7 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 8 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 9 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 10 is a diagram illustrating a PTRS allocation method.

FIG. 11 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 12 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 13 is a diagram illustrating a PTRS allocation method when a PTRScollides with a CSI-RS.

FIG. 14 is a diagram illustrating a method of configuring an intervalfor PTRS allocation.

FIG. 15 is a diagram illustrating a method of configuring an intervalfor PTRS allocation.

FIG. 16 is a diagram illustrating that block error rate (BLER)performance depends on PTRS patterns.

FIG. 17 is a diagram illustrating a PTRS allocation method.

FIG. 18 is a block diagram illustrating the configurations of a userequipment and a base station according to an embodiment of the presentdisclosure.

BEST MODE

Although the terms used in the present disclosure are selected fromgenerally known and used terms, terms used herein may vary depending onoperator's intention or customs in the art, appearance of newtechnology, or the like. In addition, some of the terms mentioned in thedescription of the present disclosure have been selected by theapplicant at his or her discretion, the detailed meanings of which aredescribed in relevant parts of the description herein. Furthermore, itis required that the present disclosure is understood, not simply by theactual terms used but by the meanings of each term lying within.

The following embodiments are proposed by combining constituentcomponents and characteristics of the present disclosure according to apredetermined format. The individual constituent components orcharacteristics should be considered optional factors on the conditionthat there is no additional remark. If required, the individualconstituent components or characteristics may not be combined with othercomponents or characteristics. In addition, some constituent componentsand/or characteristics may be combined to implement the embodiments ofthe present disclosure. The order of operations to be disclosed in theembodiments of the present disclosure may be changed. Some components orcharacteristics of any embodiment may also be included in otherembodiments or may be replaced with those of the other embodiments asnecessary.

In describing the present disclosure, if it is determined that thedetailed description of a related known function or construction rendersthe scope of the present disclosure unnecessarily ambiguous, thedetailed description thereof will be omitted.

In the entire specification, when a certain portion “comprises orincludes” a certain component, this indicates that the other componentsare not excluded and may be further included unless specially describedotherwise. The terms “unit”, “-or/er” and “module” described in thespecification indicate a unit for processing at least one function oroperation, which may be implemented by hardware, software or acombination thereof. The words “a or an”, “one”, “the” and words relatedthereto may be used to include both a singular expression and a pluralexpression unless the context describing the present disclosure(particularly, the context of the following claims) clearly indicatesotherwise.

In this document, the embodiments of the present disclosure have beendescribed centering on a data transmission and reception relationshipbetween a mobile station and a base station. The base station may mean aterminal node of a network which directly performs communication with amobile station. In this document, a specific operation described asperformed by the base station may be performed by an upper node of thebase station.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a base station, various operations performed forcommunication with a mobile station may be performed by the basestation, or network nodes other than the base station. The term basestation may be replaced with the terms fixed station, Node B, eNode B(eNB), advanced base station (ABS), access point, etc.

The term mobile station (MS) may be replaced with user equipment (UE),subscriber station (SS), mobile subscriber station (MSS), mobileterminal, advanced mobile station (AMS), terminal, etc.

A transmitter refers to a fixed and/or mobile node for transmitting adata or voice service and a receiver refers to a fixed and/or mobilenode for receiving a data or voice service. Accordingly, in uplink, amobile station becomes a transmitter and a base station becomes areceiver. Similarly, in downlink transmission, a mobile station becomesa receiver and a base station becomes a transmitter.

Communication of a device with a “cell” may mean that the devicetransmit and receive a signal to and from a base station of the cell.That is, although a device substantially transmits and receives a signalto a specific base station, for convenience of description, anexpression “transmission and reception of a signal to and from a cellformed by the specific base station” may be used. Similarly, the term“macro cell” and/or “small cell” may mean not only specific coverage butalso a “macro base station supporting the macro cell” and/or a “smallcell base station supporting the small cell”.

The embodiments of the present disclosure can be supported by thestandard documents disclosed in any one of wireless access systems, suchas an IEEE 802.xx system, a 3rd Generation Partnership Project (3GPP)system, a 3GPP Long Term Evolution (LTE) system, and a 3GPP2 system.That is, the steps or portions, which are not described in order to makethe technical spirit of the present disclosure clear, may be supportedby the above documents.

In addition, all the terms disclosed in the present document may bedescribed by the above standard documents. In particular, theembodiments of the present disclosure may be supported by at least oneof P802.16-2004, P802.16e-2005, P802.16.1, P802.16p and P802.16.1bdocuments, which are the standard documents of the IEEE 802.16 system.

Hereinafter, the preferred embodiments of the present disclosure will bedescribed with reference to the accompanying drawings. It is to beunderstood that the detailed description which will be disclosed alongwith the accompanying drawings is intended to describe the exemplaryembodiments of the present disclosure and is not intended to describe aunique embodiment which the present disclosure can be carried out.

It should be noted that specific terms disclosed in the presentdisclosure are proposed for convenience of description and betterunderstanding of the present disclosure, and the use of these specificterms may be changed to another format within the technical scope orspirit of the present disclosure.

Proposal 1 (Frequency Interval Between PTRSs)

FIG. 1 is a diagram illustrating a resource block to which ademodulation reference signal (DMRS), a PTRS, and a channel stateinformation reference signal (CSI-RS) are allocated. It may be definedthat the PTRS is allocated in the time domain and the CSI-RS isallocated in the frequency domain. For example, a collision between thePTRS and the CSI-RS may occur in a specific resource element. Inparticular, when data is transmitted in an orthogonal frequency-divisionmultiplexing (OFDM) symbol where CSI-RS transmission is reserved, thephase noise in the corresponding OFDM symbol may need to be estimated.When the PTRS collides with the CSI-RS, a method of handing such acollision may be required for phase noise estimation. Hereinafter, themethod will be described.

If no CSI-RS is defined in a PTRS region, a base station needs to informall UEs, which use the CSI-RS, that no CSI-RS is defined in the PTRSregion. However, this operation may cause signaling overhead. That is,it may not be desirable in terms of signaling overhead. On the otherhand, when no PTRS is defined in a CSI-RS region, phase noise estimationperformance may be degraded. Thus, it may be necessary to transmit theCSI-RS and the PTRS simultaneously. In the case of a UE that receivesthe CSI-RS, the UE may regard the PTRS as interference. Thisinterference problem may be solved by CSI-RS boosting. In addition, theCSI-RS may act as interference from the perspective of the PTRS.

FIG. 1 shows that when the interval between PTRSs in the frequencydomain is fixed, the PTRS collides with a specific CSI-RS port. Forexample, PTRS port #11 may collide with CSI-RS port #22 at all times.

To solve this problem, the interval between PTRS ports may be irregularas shown in FIG. 2. More specifically, PTRS port #11 may collide withCSI-RS port #22 in RB #15. In this case, since the PTRS frequencyinterval is irregular, PTRS port #11 may collide with CSI-RS port #21 inRB #17. That is, collisions may no longer occur between the same ports.That is, it is possible to solve the problem caused when a collisionoccurs at a specific port.

Proposal 1-1 (Frequency Interval Between PTRSs)

Referring to FIG. 3 CSI ports #21 to #24 are defined in the 13th OFDMsymbol, and CSI ports #25 to #28 are defined in the 14th OFDM symbol. InFIG. 3, a PTRS may be located at an interval of one OFDM symbol at thesame frequency. Although PTRS pattern #2 is assumed, the presentdisclosure is not limited thereto. The location of the PTRS may be fixedor changed for each frequency. For example, referring to FIG. 3, it canbe seen that the PTRS pattern in RB #15 is different from the PTRSpattern in RB #17. In FIG. 3, each CSI-RS port collides with a PTRS portonly once. For example, PTRS port #11 collides with each of CSI-RS ports#21 and #25 only once.

Meanwhile, using both the time-domain location of the PTRS and the PTRSinterval in the frequency domain, the number of collisions at a specificCSI-RS port may be minimized. In other words, the PTRS may be designedsuch that the collisions are distributed over all CSI-RS ports. However,the present disclosure is not limited thereto.

Proposal 1-2 (Frequency Interval Between PTRSs)

FIG. 4 illustrates a method of determining the location of a PTRS in thefrequency domain by considering a CSI-RS. Specifically, a UE may definethe PTRS or data at a (potential) PTRS location. In particular, the PTRSmay not be defined at other locations except the potential PTRSlocation. A base station may predetermine potential PTRS locations suchthat PTRS collisions are distributed over all CSI-RS ports and theninform the UE of the potential PTRS locations through at least one ofRRC, MAC-CE, and DCI.

In other words, the base station may share with the UE information on apotential region where PTRSs may be located. Thus, the PTRSs may beefficiently located.

Proposal 2 (Shifting of PTRS Frequency Location when PTRS Collides withOther Reference Signals)

If a PTRS collides with other reference signals (RSs) (e.g., CSI-RS,SRS, tracking RS, etc.), the frequency location of the PTRS may beshifted within a corresponding RB such that the PTRS is positioned at afrequency location capable of avoiding collisions with the other RSsand, at the same time, closest to the current location among frequencylocations at which a specific DMRS port in a DMRS port group associatedwith the PTRS is positioned.

For example, the frequency location of the PTRS may be shifted to afrequency location capable of avoiding collisions with other RSs andclosest to the current location among frequency locations at which aDMRS port to which the PTRS is currently mapped is positioned.

When it is said that a PTRS port is associated with a DMRS port group((1:M(>=1)), it may mean that a common phase error (CPE) or aphase-shift estimation value calculated using the PTRS port may beapplied to all DMRS ports in the DMRS port group. Meanwhile, all DMRSports in the DMRS port group may be limited to DMRS ports allocated to acorresponding UE through DCI.

When it is said that a PTRS port is associated with a DMRS port (1:1),it may mean that the PTRS port and the DMRS port use the same precoderand are defined at the same frequency location.

Specifically, referring to FIG. 5, a UE may be configured with PTRS port#1(a). Each PTRS port may be located at the lowest frequency indexwithin a corresponding RB among DMRS ports in a DMRS port groupassociated with the PTRS port. In FIG. 5, a CSI-RS port may betransmitted at a fixed frequency interval. When CSI-RS port #1 istransmitted as shown in FIG. 5, PTRS port #1(a) and CSI-RS port #1 maycollide with each other in RB #13 and RB #15. In this case, PTRS port#1(a) may be exceptionally shifted to PTRS port #1(b) in RB #13 and RB#15. PTRS port #1(b) may be positioned at the same frequency location asthat of a DMRS port associated with PTRS port #1(a). By doing so, thecollision may be avoided.

When RSs are allocated as shown in FIG. 5, the PTRS may be positioned ata subcarrier with the lowest index among frequency locations at which aDMRS port associated with the PTRS is positioned within a correspondingRB. This corresponds to type A of FIG. 5. Meanwhile, when the PTRScollides with other RSs, the PTRS may be positioned at a locationcapable of avoiding collisions with the other RSs and closest to thecurrent location among frequency locations at which a DMRS portassociated with the PTRS is positioned within a corresponding RB. Thatis, when the PTRS collides with the other RSs, the PTRS may be locatedas shown in type B of FIG. 5.

Moreover, the frequency location of the PTRS may be shifted such thatthe PTRS is positioned at a frequency location capable of avoidingcollisions with other RSs and closest to the current location amongfrequency locations at which a random DMRS port in a DMRS port groupincluding a DMRS port to which the PTRS is currently mapped ispositioned.

All DMRS ports in the DMRS port group may be limited to DMRS portsallocated to a corresponding UE through DCI.

The above-described arrangement method may be applied independently foreach RB. That is, the method may be applied independently to the PTRS ineach RB. In this case, each RB may have a different PTRS shiftingdistance. However, the present disclosure is not limited thereto.

According to the above-described arrangement method, the basic locationof the PTRS is determined as a subcarrier with the lowest index amongfrequency locations at which a DMRS port associated with the PTRS ispositioned. In contrast to the above method, the basic location may bedetermined as a subcarrier with the highest index. In this case,shifting may be performed in the opposite direction.

Consequently, the shifting location of the PTRS may be determinedimplicitly without explicit signaling as described above.

Referring to FIG. 6, a UE may be configured with PTRS port #1(a). EachPTRS port may be located at the third frequency index within acorresponding RB among DMRS ports in a DMRS port group associated withthe PTRS port. However, this is merely an example, and the presentdisclosure is not limited thereto.

In FIG. 6, CSI-RS port #1 may be transmitted at a fixed frequencyinterval. In this case, the CSI-RS may collide with PTRS port #1(a) inRB #13 and RB #15. Thus, PTRS port #1(a) may be exceptionally shifted toPTRS port #1(b) or PTRS port #1(c) in RB #13 and RB #15. PTRS port #1(b)or PTRS port #1(c) may be positioned at the same frequency location asthat of a DMRS port associated with PTRS port #1(a).

When PTRS port #1(a) is shifted to PTRS port #1(b) or PTRS port #1(c),there may be an ambiguity about shifting. In other words, an indicationabout shifting may be required. Thus, using at least one of RRC, MAC-CE,and DCI, a base station may inform a UE which one of PTRS port #1(b) orPTRS port #1(c) PTRS port #1(a) is shifted to. It may be defined as arule in specifications, but the present disclosure is not limitedthereto.

Referring to FIG. 7, when other RSs occupy the entirety (or most) of aspecific OFDM symbol within a bandwidth allocated to a UE, the UE maytransmit no PTRS in the corresponding OFDM symbol. That is, when theother RSs are allocated to the entirety or most of the specific OFDMsymbol, no PTRS transmission may be required since there is no datatransmission.

The candidate shifting locations may be restricted to DMRS portlocations having the same orthogonal cover code (OCC) or cyclic shift(CS) as that of a DMRS at the current frequency location. For example,when PTRS port #1(a) collides with other RSs in RB #13 in FIG. 7,shifting may be performed only at a location at which DMRS port #1+DMRSport #2(A) may be positioned (e.g., PTRS port #1(e)). That is, DMRS port#1—DMRS port #2(B) may be excluded from the candidate shiftinglocations, but the present disclosure is not limited thereto.

Proposal 3 (Shifting of PTRS Frequency Location when PTRS Collides withOther RSs)

When a PTRS collides with other RSs (e.g., CSI-RS, SRS, tracking RS,etc.), the frequency location of the PTRS may be shifted to a frequencylocation capable of avoiding collisions with the other RSs and closestto the current location within an RB.

Referring to FIG. 8, a UE may be configured with PTRS port #1(a). Inthis case, each PTRS port may be located at the lowest frequency indexwithin a corresponding RB among DMRS ports in a DMRS port groupassociated with the PTRS as described above.

When CSI-RS port #1 is transmitted at a fixed frequency interval asshown in FIG. 8, the CSI-RS may collide with PTRS port #1(a) in RB #13and RB #15. However, in FIG. 8, if the PTRS port is shifted according tothe method in proposal 2, the collision may still be present. In otherwords, even if a PTRS port is shifted according to the method inproposal 2, a collision may occur depending on how CSI-RS ports arearranged.

Thus, it may be considered that the PTRS is shifted to a DMRS port whichis not associated with the PTRS port. Referring to type B of FIG. 8, itcan be seen that PTRS port #1(b) is located at a frequency locationwhich is different from that of a DMRS port associated with PTRS port#1(a). In this case, PTRS port #1(b) may be shifted to a frequencylocation closest to PTRS port #1(a) within an RB.

If there is an unavoidable collision even though a PTRS port is shiftedaccording to the method in proposal 2, the method in proposal 3 may beapplied. However, the present disclosure is not limited thereto.

Specifically, in FIG. 8, the PTRS may be located at a subcarrier withthe lowest index among frequency locations at which a DMRS portassociated with the PTRS is positioned within a corresponding RB. Thisallocation may correspond to type A of FIG. 8. In this case, if it isexpected that the PTRS collides with other RSs, the PTRS may be shiftedto a different frequency location capable of avoiding collisions withthe other RSs within the corresponding RB. For example, the PTRS may beshifted to a frequency location closest to the current location. Thisallocation may correspond to type B of FIG. 8. The above-described PTRSshifting method may be applied independently to the PTRS in each RB.That is, each RB may have a different PTRS shifting distance.

According to the above-described shifting method, the basic location ofthe PTRS may be determined as a subcarrier with the lowest index amongfrequency locations at which a DMRS port associated with the PTRS ispositioned. However, the basic location may be determined as asubcarrier with the highest index, and then PTRS shifting may beperformed. In this case, the PTRS shifting may be performed in theopposite direction. Consequently, the shifting location of the PTRS maybe determined implicitly without explicit signaling as described above.

Proposal 4 (Shifting of PTRS Time-Domain Location when PTRS Collideswith Other RSs)

Referring to FIG. 9, a UE may be configured with PTRS port #1(a). EachPTRS port may be located at the lowest frequency index within acorresponding RB among DMRS ports in a DMRS port group associated withthe PTRS port as described above. For example, if CSI-RS port #1 isallocated and transmitted at a fixed frequency interval, there may be acollision between PTRS and CSI-RS ports. Referring to FIG. 9, it can beseen that PTRS port #1(a) collides with the CSI-RS port in RB #13 and RB#15.

For example, type A of FIG. 9 shows the current location of a PTRS, andtype B of FIG. 9 shows that while the frequency location of the PTRS isfixed, the time-domain location thereof is shifted. The PTRS locationmay be shifted in the time domain as shown in FIG. 9.

Among proposals 2 to 4, proposal 2 may be preferentially applied. ThePTRS port may be shifted to the location corresponding to the lowestindex among DMRS ports in a DMRS port group. That is, the shifting maybe performed first in the frequency domain. However, when there is anunavoidable collision even though the PTRS shifting is performed basedon CSI-RS patterns, proposals 3 and 4 may be selectively applied.

When the PTRS is located at an interval of one or more symbols (i.e.,pattern #2), if there is an unavoidable collision even though proposal 2is applied, the PTRS shifting may be performed according to proposal 4.That is, due to the symbol gap between the PTRSs, the shifting may beperformed in the time domain, thereby avoiding the collision.

In this case, the shifting location in the time domain may be equallyapplied to all resource blocks allocated to the UE through DCI.

Meanwhile, when the PTRS is located at all symbols (i.e., pattern #1),if there is an unavoidable collision even though proposal 2 is applied,the PTRS shifting may be performed according to proposal 3. That is,since the PTRS cannot be shifted in the time domain, the shifting needsto be performed to the closest frequency location as described inproposal 3.

It may be configured that proposal 2 has the highest priority, proposal4 has the second highest priority, and proposal 3 has the third highestpriority.

In summary, the PTRS may be shifted according to proposal 2. If there isan unavoidable collision, the PTRS may be shifted in the time domainaccording to proposal 4. If the unavoidable collision is still presentafter the PTRS is shifted in the time domain, the PTRS may be shiftedagain to the closest frequency location according to proposal 3.However, the present disclosure is not limited thereto.

Proposal 5 (PTRS Location Signaling)

A base station may inform a UE of the time-domain location of a PTRSusing at least one of RRC, MAC-CE, and DCI.

Referring to FIG. 10, PTRS pattern #2 may have two types: type A andtype B. In type A, the PTRS may be located at an interval of one or moresymbols starting from the time-domain location at which a DMRS port islocated. In type B, the PTRS may be located at an interval of one ormore symbols starting from a symbol beyond the time-domain location atwhich a DMRS port is located.

In this case, the base station may inform the UE which one of the twopatterns is to be used through at least one of the RRC, MAC-CE, and DCI.Further, the base station may configure another pattern and inform theUE that the pattern is to be used. However, the present disclosure isnot limited thereto.

Proposal 6 (PTRS Location Signaling)

A base station may set the time-domain interval between PTRSs to beequal to or more than 2 in a slot (or subframe) where a CSI-RS istransmitted and then inform a UE of the time-domain interval through atleast one of RRC, MAC-CE, and DCI. In addition, the base stationtransmits the CSI-RS in an OFDM symbol where no PTRS is defined.

FIG. 11 shows PTRS pattern #2. That is, FIG. 11 shows that thetime-domain interval between PTRSs is 2. In this case, the base stationmay allocate the PTRS such that it does not overlap with the CSI-RS.Meanwhile, since PTRS pattern #2 shows performance similar to that ofPTRS pattern #1 in most modulation and coding scheme (MCS) levels,allocation may be performed as described above.

Meanwhile, the base station may inform the UE that CSI-RSs aretransmitted in specific slots in a specific frame through at least oneof the RRC, MAC-CE, and DCI. In this case, the UE does not use PTRSpattern #1 in the corresponding slots. In other words, the PTRS may notbe allocated to all slots.

When PTRS pattern #1 (PTRS time-domain interval=1) is not defined, theabove-mentioned signaling may not be required.

When the PTRS is defined as described above, the CSI-RS may betransmitted in a random OFDM symbol where no PTRS is defined. AlthoughFIG. 11 shows that the CSI-RS is transmitted in symbols #11 and 13, theCSI-RS may be transmitted in symbols #3, 5, 7, 9, 11, and 13.

Referring to FIG. 12, the OFDM symbol in which the CSI-RS is to betransmitted may be punctured for the PTRS. In this case, if data is nottransmitted in the OFDM symbol in which the CSI-RS is to be transmitted,phase noise estimation may not be required in the corresponding OFDMsymbol. Thus, there is no performance degradation due to puncturing.

Although FIG. 12 shows that the CSI-RS is allocated to symbols #11 and13, the CSI-RS may be allocated to other locations and then transmittedas described above. In this case, the PTRS may be punctured at thelocations where the CSI-RS is to be transmitted. However, the presentdisclosure is not limited thereto.

Proposal 7 (PTRS Puncturing)

If a PTRS overlaps with a CSI-RS in a specific OFDM symbol, the PTRS maybe punctured. In this case, an additional PTRS may be transmitted in aregion where there is no overlap therebetween. A base station may informa UE of a method of defining the additional PTRS, using at least one ofRRC, MAC-CE, and DCI. Alternatively, the method of defining theadditional PTRS may be defined as a rule in specifications.

FIG. 13 illustrates that PTRSs collide with CSI-RSs in RBs #15 to #17and no CSI-RS is transmitted in RB #14. In this case, an additional PTRSmay be defined and transmitted in RB #14 where no CSI-RS is transmitted.The additional PTRS is defined and transmitted as follows. First, adifference between the number of PTRSs required in one OFDM symbol andthe number of valid PTRSs therein is calculated. Then, the additionalPTRS may be transmitted based on the difference. FIG. 13 shows thatthree PTRSs are required since there are a total of three collisions inRBs #15 to 17. In this case, the PTRSs may be sequentially defined atthe top and bottom of the original position and then transmitted.

In addition, it may be considered that RB #13 is additionally allocated.If no CSI-RS is transmitted even in RB #13, two additional PTRSs may bedefined and transmitted in each of RBs #13 and #14.

In proposals 1 to 7, methods of minimizing or avoiding a collisionbetween a signal defined in the frequency domain such as the CSI-RS anda signal defined in the time domain such as the PTRS have beendescribed. Meanwhile, considering that the SRS is also defined in thefrequency domain, it may collide with an uplink (UL) PTRS. Therefore,proposals 1 to 7 may be equally applied to the SRS and UL PTRS.

In addition, in the case of ultra-reliable and low-latencycommunications (URLLC), data may be transmitted in one or two OFDMsymbols. In this case, the data may collide with the PTRS, and thus themethods in proposals 1 to 7 may be equally applied to solve thecollision problem.

In summary, proposals 1 to 7 may be applied when a PTRS collides with asignal defined in the frequency domain (e.g., SRS, CSI-RS, etc.) or data(e.g., URLLC), but the present disclosure is not limited thereto.

Proposal 8 (Priority with Regard to PTRS Depending on CSI-RS Type)

The priority with regard to the PTRS may be determined based on CSItypes. In the case of a zero-power (ZP) CSI-RS, since it is explicitlydefined by a base station that rate-matching is performed on acorresponding part, the ZP CSI-RS may have the highest priority. Thatis, when the PTRS collides with the ZP CSI-RS, the PTRS may not betransmitted. In the case of an aperiodic non-zero-power (NZP) CSI-RS, ifthe base station explicitly instructs a UE to perform CSI estimationthrough the NZP CSI-RS, it may have a higher priority than the PTRS.

In the case of a periodic NZP CSI-RS with measurement restrictions, theUE may transmit the CSI-RS periodically. In this case, if there aremeasurement restrictions, since it cannot be averaged with previous CSI,the impact of a collision with the PTRS may increase. Thus, the periodicNZP CSI-RS with measurement restrictions may have a higher priority thanthe PTRS.

In the case of a periodic NZP CSI-RS with no measurement restriction,the UE may transmit the CSI-RS periodically. In this case, since it maybe averaged with previous CSI, although some REs are damaged, the impactmay not be significant. Thus, in the case of aperiodic CSI-RStransmission, the PTRS may be transmitted instead of the CSI-RS.However, another UE that does not use the PTRS cannot know whether someREs are used for PTRS transmission if there is no separate signalling.Thus, the CSI-RS and PTRS may be simultaneously transmitted. In thiscase, proposals 1 to 8 may be used to avoid a collision, but the presentdisclosure is not limited thereto.

The bandwidth in which a NZP CSI-RS is transmitted may occupy most ofthe bandwidth allocated for the UE. In this case, it is not necessary toperform channel estimation on a corresponding OFDM symbol. That is, thePTRS may not be transmitted, and thus, no collision may occur.

Regardless of the measurement restrictions, the PTRS may not betransmitted in the OFDM symbol and bandwidth where the NZP CSI-RS istransmitted.

In the case of UL, a ZP SRS may be introduced for UL interferencemeasurement or rate-matching. In addition, the measurement restrictionmay be introduced for a NZP SRS. Moreover, periodic SRS transmission oraperiodic SRS transmission may also be considered. In this case, thepriorities of the ZP SRS, aperiodic NZP SRS, periodic NZP CSI-RS withmeasurement restrictions, and periodic NZP CSI-RS with no measurementrestriction with regard to the PTRS may be applied in the same way as inthe case of the CSI-RS. However, the present disclosure is not limitedthereto.

Proposal 9 (Determination of PTRS Time-Domain Location)

The location of a PTRS in the time domain may be determined. Referringto FIG. 14, each of a, b1, and b2 may mean an interval between adjacentPTRSs. In this case, the number of PTRSs in the time domain may bechanged (e.g., when the number of PTRSs is N, an interval may be definedas b_(N−1)), where a is determined by the magnitude of a residualcarrier frequency offset (CFO) and b1 and b2 are determined by at leastone of an MCS, a bandwidth, a center frequency, and subcarrier spacing.

FIG. 15 illustrates four PTRS time-domain patterns. If the residual CFOis large, a may have a small value. Each of patterns #3 and #4 of FIG.15 may correspond to a case where the value of a is small.

If the residual CFO is small, a may have a large value. Pattern #1 ofFIG. 15 may correspond to a case where the value of a is large. That is,the distance from the time-domain location at which the DMRS isallocated to the PTRS may increase.

When the residual CFO is large and when at least one of the bandwidthand the MCS is also large, the values of a and b may decrease. Pattern#2 of FIG. 15 may correspond to a case where both a and b have smallvalues. However, the RS overhead may be highest.

FIG. 16 illustrates simulation results in the above case. Specifically,FIG. 16 shows block error rate (BLER) performance depending on the useof a PTRS when there is a residual CFO (100 Hz, 300 Hz, 3 kHz) and phasenoise. In this case, the MCS and coding rate may be QPSK and ½,respectively. Referring to FIG. 16, it can be seen that when theresidual CFO is 300 Hz, the BLER performance is similar regardless ofwhether the PTRS is used. In other words, when the residual CFO issmall, the performance is similar regardless of whether the PTRS isused.

Meanwhile, when the residual CFO is 3 kHz, the performance maysignificantly vary depending on the presence or absence of the PTRS.Since pattern #2 of FIG. 15 has the densest structure than otherpatterns, it shows the most stable performance. In the case of patterns#1 and #4, the performance may be significantly degraded due to aninsufficient number of PTRSs.

In the case of pattern #1, since the distance between the DMRS and thesecond PTRS in the time domain is relatively long, the residual CFO maynot be estimated due to the long distance, and as a result, theperformance may be significantly degraded. Meanwhile, in the case ofpattern #4, since the distance between the DMRS and the second PTRS inthe time domain is relatively short, the residual CFO may besuccessfully estimated. However, the estimated residual CFO may includethe value of CPE_3 (the CPE value of OFDM symbol 3). For example, in thecase of residual CFO=0.1 and CPE_3=0.01, the actually estimated residualCFO may have a value of 0.11. In this case, the phase rotation errorshown in Equation 1 may occur in an n-th OFDM symbol (where n>2).

$\begin{matrix}{{Error} = {{{\left( {n - 2} \right) \times {Residual}\mspace{14mu}{CFO}} + {CPE\_ n} - {\left( {n - 2} \right) \times \left( {{{Residual}\mspace{14mu}{CFO}} + {{CPE\_}3}} \right)}} = {{CPE\_ n} - {\left( {n - 2} \right) \times {CPE\_}3\mspace{14mu}\left( {n > 2} \right)}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In the case of n=3, the error may be zero. However, as n increases, theerror may continuously increase. Thus, in the case of pattern #4, as nincreases, the performance may be further degraded due to the channelestimation error in the n-th OFDM symbol.

In the case of pattern #3, since the second PTRS is closer compared topattern #1, there is no failure in the residual CFO estimation so thatthe performance degradation may not occur.

In the case of pattern #1, after estimation of the residual CFO based onthe first PTRS, the residual CFO is pre-compensated for according to themethod described with reference to pattern #4. In addition, if the CPEis estimated using the second PTRS in the pre-compensated state, theperformance of pattern #1 may be similar to that of pattern #3. That is,by changing the method of estimating the residual CFO and CPE, theperformance of pattern #1 may be improved.

Considering that pattern #1 is denser than pattern #3 in the timedomain, pattern #1 may provide better performance than pattern #3 whenthe environment is sensitive to the phase noise due to a high MCS or alarge bandwidth.

Since in the case of pattern #3, the first PTRS is closer to the DMRScompared to pattern #1, pattern #3 has a low estimation failureprobability when the residual CFO is large. In particular, if the SNR islow and the residual CFO is large, the failure probability may increase,but it may be minimized in the above manner. The present disclosure isnot limited thereto.

FIG. 17 is a flowchart illustrating a PTRS allocation method.

A base station may generate a PTRS and a first RS (S1710). As describedwith reference to FIGS. 1 to 16, the first RS may include at least anyone of a CSI-RS, an SRS, and a tracking RS. That is, the first RS maymean another RS, and the present disclosure is not limited thereto.

Next, the PTRS and the first RS may be allocated to an RB (S1720). Asdescribed with reference to FIGS. 1 to 16, the PTRS may be allocated onthe same frequency. In this case, the PTRS may be allocated at aninterval of at least one OFDM symbol. Alternatively, the PTRS may beallocated to all OFDM symbols as described above.

Thereafter, the base station may transmit the allocated PTRS and firstRS to a UE (S1730). As described with reference to FIGS. 1 to 16, whenthe PTRS collides with the first RS in the RB, the frequency location ofthe PTRS may be shifted. In this case, the PTRS frequency location maybe shifted to a frequency location closest to the current PTRS frequencylocation among frequency locations at which DMRS ports in the DMRS portgroup associated with the PTRS are positioned. By doing so, it ispossible to avoid the collision between the PTRS and the first RS. Theshifted PTRS frequency location may be indicated through at least anyone of RRC, MAC-CE, and DCI.

When a frequency location capable of avoiding the collision with thefirst RS is not found among the frequency locations at which the DMRSports in the DMRS port group associated with the PTRS are positioned,the PTRS may be positioned at a frequency location capable of avoidingthe collision among frequency locations closest to the current PTRSfrequency location. That is, the PTRS frequency location may be shiftedto a frequency location capable of avoiding the collision where no DMRSport is allocated as described above.

When the PTRS collides with the first RS, the frequency location of thePTRS may be fixed and the time-domain location thereof may be shifted.This method may be applied only when the PTRS is allocated at aninterval of at least one OFDM symbol at one frequency.

When the frequency location capable of avoiding the collision with thefirst RS is not found among the frequency locations at which the DMRSports in the DMRS port group associated with the PTRS are positioned, ifthe PTRS is allocated at an interval of at least one OFDM symbol at onefrequency, the frequency location of the PTRS may be fixed and thetime-domain location thereof may be shifted. On the other hand, when thefrequency location capable of avoiding the collision with the first RSis not found among the frequency locations at which the DMRS ports inthe DMRS port group associated with the PTRS are positioned, if the PTRSis allocated to all OFDM symbols at one frequency, the frequencylocation of the PTRS may be shifted to the frequency location capable ofavoiding the collision among the frequency locations closest to thecurrent PTRS frequency location.

In addition, shifting methods may be prioritized. For example, shiftingin the frequency locations at which the DMRS ports in the DMRS portgroup may have the highest priority, shifting of the time-domainlocation may have the second highest priority, and shifting of thefrequency-domain location may have the lowest priority as describedabove.

Device Configuration

FIG. 18 is a block diagram showing the configuration of a user equipmentand a base station according to one embodiment of the presentdisclosure. In FIG. 18, the user equipment 100 and the base station 200may include radio frequency (RF) units 110 and 210, processors 120 and220 and memories 130 and 230, respectively. Although a 1:1 communicationenvironment between the user equipment 100 and the base station 200 isshown in FIG. 18, a communication environment may be established betweena plurality of user equipment and the base station. In addition, thebase station 200 shown in FIG. 18 is applicable to a macro cell basestation and a small cell base station.

The RF units 110 and 210 may include transmitters 112 and 212 andreceivers 114 and 214, respectively. The transmitter 112 and thereceiver 114 of the user equipment 100 are configured to transmit andreceive signals to and from the base station 200 and other userequipments and the processor 120 is functionally connected to thetransmitter 112 and the receiver 114 to control a process of, at thetransmitter 112 and the receiver 114, transmitting and receiving signalsto and from other devices. The processor 120 processes a signal to betransmitted, sends the processed signal to the transmitter 112 andprocesses a signal received by the receiver 114.

If necessary, the processor 120 may store information included in anexchanged message in the memory 130. By this structure, the userequipment 100 may perform the methods of the various embodiments of thepresent disclosure.

The transmitter 212 and the receiver 214 of the base station 200 areconfigured to transmit and receive signals to and from another basestation and user equipments and the processor 220 are functionallyconnected to the transmitter 212 and the receiver 214 to control aprocess of, at the transmitter 212 and the receiver 214, transmittingand receiving signals to and from other devices. The processor 220processes a signal to be transmitted, sends the processed signal to thetransmitter 212 and processes a signal received by the receiver 214. Ifnecessary, the processor 220 may store information included in anexchanged message in the memory 230. By this structure, the base station200 may perform the methods of the various embodiments of the presentdisclosure.

The processors 120 and 220 of the user equipment 100 and the basestation 200 instruct (for example, control, adjust, or manage) theoperations of the user equipment 100 and the base station 200,respectively. The processors 120 and 220 may be connected to thememories 130 and 230 for storing program code and data, respectively.The memories 130 and 230 are respectively connected to the processors120 and 220 so as to store operating systems, applications and generalfiles.

The processors 120 and 220 of the present disclosure may be calledcontrollers, microcontrollers, microprocessors, microcomputers, etc. Theprocessors 120 and 220 may be implemented by hardware, firmware,software, or a combination thereof.

If the embodiments of the present disclosure are implemented byhardware, Application Specific Integrated Circuits (ASICs), DigitalSignal Processors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), etc. may be included in the processors 120 and 220.

In the case of implementation by firmware or software, a methodaccording to each embodiment of the present disclosure can beimplemented by modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code is stored in thememory unit and is then drivable by the processor. The memory unit isprovided within or outside the processor to exchange data with theprocessor through the various means known to the public.

The detailed description of the preferred embodiments of the presentdisclosure has been given to enable those skilled in the art toimplement and practice the disclosure. Although the disclosure has beendescribed with reference to the preferred embodiments, those skilled inthe art will appreciate that various modifications and variations can bemade in the present disclosure without departing from the spirit orscope of the disclosure described in the appended claims. Accordingly,the disclosure should not be limited to the embodiments described hereinbut should be accorded the broadest scope consistent with the principlesand novel features disclosed herein. It will be apparent that, althoughthe preferred embodiments have been shown and described above, thepresent specification is not limited to the above-described specificembodiments, and various modifications and variations can be made bythose skilled in the art to which the present disclosure pertainswithout departing from the gist of the appended claims. Thus, it isintended that the modifications and variations should not be understoodindependently of the technical spirit or prospect of the presentspecification.

The embodiments of both the method and device have been described inthis document, and if necessary, the descriptions thereof may becomplementarily applied.

INDUSTRIAL APPLICABILITY

The above-described embodiments are applicable not only to the 3GPP LTEand LTE-A systems but also to various wireless communication systemsincluding IEEE 802.16x and IEEE 802.11x systems. Further, the proposedmethods are applicable to an mmWave communication system usingultra-high frequency band.

The invention claimed is:
 1. A method of transmitting a reference signalby a base station in a wireless communication system, the methodcomprising: transmitting configuration information including informationon a resource region of a zero power channel state information-referencesignal (CSI-RS); generating a phase tracking reference signal (PTRS);allocating the PTRS to a resource block and transmitting the allocatedPTRS, wherein when a resource region to which the PTRS is allocatedcollides with the resource region of the zero power CSI-RS within theresource block, the PTRS is not transmitted in a colliding resourceregion.
 2. The method of claim 1, wherein when the resource region towhich the PTRS is allocated collides with the resource region of thezero power CSI-RS within the resource block, the PTRS is not allocatedto the colliding resource region.
 3. The method of claim 1, wherein whenthe resource region to which the PTRS is allocated collides with theresource region of the zero power CSI-RS within the resource block, thezero power CSI-RS is transmitted in the colliding resource region. 4.The method of claim 1, wherein the configuration information includingthe information on the resource region of the zero power CSI-RS istransmitted in at least one of radio resource control (RRC) and adownlink control indicator (DCI).
 5. A base station for transmitting areference signal in a wireless communication system, the base stationcomprising: a transmitter configured to transmit a signal; and aprocessor configured to control the transmitter, wherein the processoris configured to: control the transmitter to transmit configurationinformation including information on a resource region of a zero powerchannel state information-reference signal (CSI-RS); generate a phasetracking reference signal (PTRS); allocate the PTRS to a resource blockand transmit the allocated PTRS, and wherein when a resource region towhich the PTRS is allocated collides with the resource region of thezero power CSI-RS within the resource block, the PTRS is not transmittedin a colliding resource region.
 6. The base station of claim 5, whereinwhen the resource region to which the PTRS is allocated collides withthe resource region of the zero power CSI-RS within the resource block,the PTRS is not allocated to the colliding resource region.
 7. The basestation of claim 5, wherein when the resource region to which the PTRSis allocated collides with the resource region of the zero power CSI-RSwithin the resource block, the zero power CSI-RS is transmitted in thecolliding resource region.
 8. The base station of claim 5, wherein theconfiguration information including the information on the resourceregion of the zero power CSI-RS is transmitted in at least one of radioresource control (RRC) and a downlink control indicator (DCI).